<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>box-sizing</title>
  <style>
  .box {
    width: 200px;
    height: 100px;
    padding: 20px;
    border: 5px solid black;
    margin: 20px;
  }
  .border-box {
    /* border padding 先分配，剩余的是内容大小
      多列布局的时候有优势
    */
    background-color: lightblue;
    box-sizing: border-box;
  }
  .content-box {
    background-color: lightgreen;
    box-sizing: content-box;
  }
  </style>
</head>
<body>
<div class="box border-box">Border with border-box</div>
<div class="box content-box">Box with content-box</div>
</body>
</html>